1. Field of the Invention
The present invention relates to an antenna-coupled module which is suitable to be used as a small transmission and reception unit for communication or broadcasting.
2. Description of the Related Art
Recently, accompanying with developments of wireless communication technologies, various electronic equipments or wireless cards into each of which a small transmission and reception unit is incorporated are suggested. As the transmission and reception unit, conventionally, an antenna-coupled high frequency module having an antenna element provided on a circuit board on which a high frequency circuit is provided is known. In the conventional antenna-coupled module, it is common that a predetermined area on the circuit board on which main parts of the high frequency circuit are provided is covered with a shield case made of a metal plate and the antenna element such as a chip antenna or a pattern antenna is provided at another area on the circuit board.
In such a conventional antenna-coupled module, the high frequency circuit comprises a wiring pattern formed on an upper surface of the circuit board, various circuit components, such as chip components or ICs, connected to the wiring pattern, and a ground conductor formed on a bottom surface or an inner layer of the circuit board, in which a portion of the wiring pattern extends outside the shield case to be connected to a feeding portion of the antenna element. Further, the ground conductor is connected to a ground portion of the antenna element through a via hole formed in the circuit board. Simultaneously, the ground conductor is also connected to the shield case. The shield case is mounted to the circuit board while covering the main parts of the high frequency circuit, such that the high frequency circuit is almost electromagnetically shielded (for example, see Japanese Unexamined Patent Application Publication No. 2002-232221 (FIG. 1, p. 4–6)).
As described above, in the conventional antenna-coupled module, the antenna element and the shield case are provided on the circuit board in parallel and the shield case covers the main parts of the high frequency circuit. Thus, even if the shield case and the antenna element are arranged as nearly as possible, the size of the module increases somewhat as a whole in a plan view, which results in a problem in that it is difficult to achieve miniaturization. Further, in the conventional antenna-coupled module, since the space for the antenna element is narrow, there may be many cases in which an additional antenna element such as a chip antenna is needed to be mounted on the circuit board so as to a desired electric field in a radiating conductive portion.
Therefore, there is a problem in that the number of the components increases, which consequently increases the manufacturing cost of the module.